European Southern Observatory Tests Spectroscope for High-Quality Imaging

The Adaptive Optics Facility (AOF) on the European Southern Observatory (ESO) tested instruments for Unit Telescope 4 (UT4) as part of its Multi-Unit Spectroscopic Explorer (MUSE) for high-quality imaging of celestial objects.

This image shows a small fraction of the total data collected by the MUSE using the AOF system and demonstrates the increased abilities of the new AOF-equipped MUSE instrument. Courtesy of J. Richard/ESO.

The AOF is a long-term project on the ESO’s Very Large Telescope, which has been coupled with MUSE, an integral-field spectrograph. Adaptive optics work to compensate for the blurring effect of the Earth's atmosphere, enabling MUSE to obtain much sharper images and resulting in twice the contrast previously achievable. MUSE can now study even fainter objects in the universe.

"Now, even when the weather conditions are not perfect, astronomers can still get superb image quality thanks to the AOF," said Harald Kuntschner, AOF project scientist at ESO.

Astronomers were able to observe the planetary nebulae IC 4406, located in the constellation Lupus (The Wolf), and NGC 6369, located in the constellation Ophiuchus (The Serpent Bearer). The MUSE observations using the AOF showed dramatic improvements in the sharpness of the images, revealing never-before-seen shell structures in IC 4406.

One thousand times per second, the AOF system calculates the correction that must be applied to change the shape of the telescope's deformable secondary mirror to compensate for atmospheric disturbances. In particular, the Ground Atmospheric Layer Adaptive Corrector for Spectroscopic Imaging (GALACSI) corrects for the turbulence in the layer of atmosphere up to one kilometer above the telescope. Depending on the conditions, atmospheric turbulence can vary with altitude, but studies have shown that the majority of atmospheric disturbance occurs in this ground layer of the atmosphere.

"The AOF system is essentially equivalent to raising the VLT about 900 meters higher in the air, above the most turbulent layer of atmosphere," said Robin Arsenault, AOF project manager. "In the past, if we wanted sharper images, we would have had to find a better site or use a space telescope – but now with the AOF, we can create much better conditions right where we are, for a fraction of the cost.”

ESO is an intergovernmental astronomy organization and ground-based astronomical observatory supported by the countries of Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the U.K., along with the host state of Chile.